Every vs. Weekly

As far as I can tell, there is no functional difference between setting a task to repeat "Every Mon" as opposed to "Weekly", it seems counterintuitive to have the option in there if it's not going to behave as expected....

If I create a task to repeat "every mon", and I move the start date or due date to a wednesday because I don't plan on doing it that day
(deferral), then when I finally check it off, and it reschedules itself, I would expect it to appear on the following Monday. Instead it appears on the following wednesday (ie one week from the due date). Therefor it is functioning as "weekly" instead of "every mon".